This invention relates to exhaust systems and, in particular, to mufflers for quieting the exhaust noise of a vehicle engine. More particularly, this invention relates to mufflers having outer shells and a single inner cartridge situated between the outer shells to define a plurality of tubes and chambers between the outer shells.
It is known to construct mufflers using stamp-formed outer shells and inner plates. See, for example, U.S. Pat. No. 5,252,788 to Emrick et al.; U.S. Pat. No. 5,229,557 to Allman et al.; U.S. Pat. No. 5,147,987 to Richardson et al.; U.S. Pat. No. 5,004,069 to Van Blaircum et al.; U.S. Pat. No. 4,941,545 to Wilcox et al.; U.S. Pat. No. 4,860,853 to Moring; U.S. Pat. No. 4,736,817 to Harwood; and U.S. Pat. No. Re. 33,370 to Harwood.
Stamp-formed mufflers include a plurality of chambers and tubes formed between the stamped outer shells and inner plates. The chambers and tubes direct exhaust gas of the vehicle engine through the muffler in a desired manner to quiet the exhaust noise produced by the vehicle engine effectively.
Various techniques have been used to form tubes and chambers in stamp-formed mufflers. For example, in U.S. Pat. No. 5,229,557 to Allman et al.; U.S. Pat. No. 5,147,987 to Richardson et al.; and U.S. Pat. No. 4,941,545 to Wilcox et al., drop-in baffles were placed between the inner plates and outer shells to form chambers within the muffler. Also, for example, in U.S. Pat. No. 4,860,853 to Moring; U.S. Pat. No. 4,736,817 to Harwood; U.S. Pat. No. 5,004,069 to Van Blaircum et al.; and U.S. Pat. No. Re 33,370 to Harwood the outer shells are "deep-drawn" to define a crease in the outer shells that extends inwardly to abut the inner plates and form chambers within the muffler. In U.S. Pat. No. 5,252,788 to Emrick et al., the inner plates are deep-drawn outward to abut the outer shells that are deep-drawn inward to form chambers within the muffler. The sheet metal deep-drawing process is an expensive manufacturing process that is difficult to perform with accuracy on stainless steel sheet metal.
What is needed is a stamp-formed muffler that is manufactured without using a deep-drawing process on the outer shells to define chambers in the muffler. A stamp-formed muffler having a minimum number of parts is also needed. A muffler manufactured without a deep-drawing process to define chambers and with a minimum number of parts would reduce the time and cost of manufacturing and assembly.
According to the present invention, a muffler is provided having a top outer shell, a bottom outer shell, and a drop-in inner cartridge. The top outer shell includes a top wall, a lip, spaced-apart first and second side walls extending between the top wall and the lip, and spaced-apart first and second end walls extending between the first and second side walls, top wall, and lip. The bottom outer shell includes a bottom wall, a lip, spaced-apart first and second side walls extending between the bottom wall and the lip, and spaced-apart first and second end walls extending between the first and second side walls, bottom wall, and lip.
The lips of the top and bottom outer shells cooperate to define an interior cartridge-receiving chamber. The lip of the top outer shell abuts the lip of the bottom outer shell to define a seam that includes an inner surface facing into the interior cartridge-receiving chamber. The drop-in inner cartridge is positioned to lie between the top and bottom outer shells. The drop-in inner cartridge extends from the first side wall of the top and bottom outer shells to the second side wall of the top and bottom outer shells. The drop-in inner cartridge further includes an outer edge abutting the inner surface of the seam to cause the drop-in inner cartridge to lie wholly within the interior cartridge-receiving chamber.
In a preferred embodiment of the present invention, the drop-in inner cartridge includes an inlet tube, an outlet tube, and first, second, and third baffles extending between the inlet and outlet tubes. The inlet and outlet tubes and the first, second, and third baffles define first, second, third, and fourth chambers. Various apertures and louvers are formed in the inlet tube, outlet tube, and baffles. Gas flow entering the inlet tube passes from the inlet tube serially through the first chamber, second chamber, third chamber, and fourth chamber and into the outlet tube.
In another preferred embodiment of the present invention, the drop-in inner cartridge includes first, second, and third baffles to define first and second helmholtz tuning chambers and first and second flow-through chambers. Gas flow entering the inlet tube passes from the inlet tube serially through the first and second flow-through chambers and into the outlet tube. The first flow-through tuning chamber is in direct communication with the first Helmholtz tuning chamber and the second flow-through tuning chamber is in direct communication with the second Helmholtz tuning chamber.
In another preferred embodiment of the present invention, the drop-in inner cartridge includes a single baffle extending between the inlet tube and the outlet tube to define first and second chambers. Gas flow entering the inlet tube passes from the inlet tube serially through the first and second chambers and into the outlet tube.
In preferred embodiments of the present invention, the drop-in inner cartridge includes a baffle system extending between the inlet tube and the outlet tube. Each of the inlet and outlet tubes include a top side facing upwardly toward the top outer shell and a bottom side facing downwardly toward the bottom outer shell. The baffle system includes a first side connected to one of the top and bottom sides of the inlet tube and a second side connected to the other of the top and bottom sides of the outlet tube.
In yet another preferred embodiment of the present invention, the drop-in inner cartridge includes a plurality of tubes and a baffle connected to the plurality of tubes. The baffle extends substantially parallel to a longitudinal axis of the muffler between the first end walls of the top and bottom outer shells and the second end walls of the top and bottom outer shells. The baffle also extends between the top wall of the top outer shell and the bottom wall of the bottom outer shell to lie substantially perpendicular to the top wall of the top outer shell and the bottom wall of the bottom outer shell.
In most embodiments of the present invention, the muffler assembly consists of only three pieces. The three-piece muffler assembly consists of only a stamped top outer shell, a stamped bottom outer shell, and a drop-in inner cartridge situated between the top and bottom stamped outer shells.
In some embodiments of the present invention, one or more tuning throats may be connected to one or more of the baffles and extend into a chamber. The tuning throat provides additional tuning to quiet the exhaust gas flow.
In some embodiments of the present invention, the muffler assembly consists of only two pieces. The two-piece muffler assembly consists of only a single outer shell and a single drop-in inner cartridge. The single outer shell is made from a flat sheet of material using a stamping process. The stamped single outer shell is then folded to surround the single drop-in inner cartridge.
In all embodiments of the present invention, no deep-drawing operations are required to make creases in the top and bottom stamped outer shells or the drop-in inner cartridge to define chambers between the stamped outer shells. The top and bottom stamped outer shells are formed to include stiffening ribs. However, these stiffening ribs do not define chambers between the stamped outer shells. By producing a stamp-formed muffler without using a deep-drawing process to define chambers, the manufacturing cost of the muffler is minimized.
A single sheet of material is used to manufacture the drop-in inner cartridge which provides baffles to define the chambers and inlet and outlet tubes. The baffles also provide significant structural support for the muffler.
The drop-in inner cartridge is made from a single pre-cut sheet of material according to the following steps. The various apertures and louver patches present in the inlet and outlet tubes and the baffles are extruded in the pre-cut sheet of material. Next, a break-and-fold process is performed on the single flat sheet of material to form the baffles. Finally, the sides of the pre-cut sheet of material are rolled to form the inlet and outlet tubes. In embodiments of the present invention having a single baffle, the break-and-fold process is not required.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.